1. Field of the Invention
The present invention relates generally to state transition in a mobile communication system, and in particular, to a method of controlling the change of a radio physical channel caused by transition between an active mode and a control hold mode in a traffic channel substate of a mobile station or a base station in the base station.
2. Description of the Related Art
A conventional CDMA (Code Division Multiple Access) mobile communication system provides primarily voice service. From this CDMA mobile communication system, IMT (International Mobile Telecommunication)-2000 standards have been evolved. An IMT-2000 mobile communication system is capable of additionally providing a high quality voice service, a moving picture service, Internet browsing, and various other data communications.
The standard CDMA mobile communication system is comprised of a base station (BS) having a base station transceiver system (BTS) and a base station controller (BSC), a mobile switching center (MSC), and a mobile station (MS). Radio links between the MS and the BTS are a forward link on which data is directed from the BTS to the MS and a reverse link on which data is directed from the MS to the BTS.
All channels are grouped into physical channels and logical channels. A logical channel is established on a physical channel. It is possible to establish a plurality of logical channels on one physical channel. If the physical channel is released, the logical channels are also released. A physical channel is not necessarily established prior to establishment of a logical channel. When an intended physical channel is set up for another logical channel, all that should be done is to allocate a logical channel in question on the established physical channel.
The physical channels are divided into dedicated channels and common channels according to their natures. The dedicated channels are dedicated to communications between a BTS and an MS, including a fundamental channel (FCH), a dedicated control channel (DCCH), and a supplemental channel (SCH). The FCH is commonly used to transmit data according to the for TIA/EIA-95-B standard and transmits a voice signal, a data signal, and a signaling signal (or a control signal). The DCCH transmits a data signal and a signaling signal. The SCH transmits a large amount of data. All other physical channels except the dedicated channels are common channels. The common channels are shared commonly by a plurality of MSs to communicate with a BTS. A physical channel on a forward link is a paging channel and a physical channel on a reverse link is an access channel. These common channels are compatible with the IS-95-B standard.
Dedicated logical channels allocated on the physical channels are a dedicated signaling channel (DSCH) and a dedicated traffic channel (DTCH). The DSCH can be allocated on an FCH and a DCCH. On the DTCH can be allocated all of the FCH, DCCH, and SCH information. The DSCH is so called because it transmits a control signal between a BTS and an MS. The DTCH is used to transmit user data between the BTS and the MS. Common logical channels allocated on the common physical channels are a common signaling channel (CSCH) for transmitting a signaling signal and a common traffic channel (CTCH) for transmitting user data. The common logical channels are allocated on the paging channel for the forward link and on the access channel for the reverse link.
In the CDMA mobile communication system, packet data communication is characterized in that transmission of burst data alternates with long non-transmission periods. Connection of a channel only at a data transmission starting point has been suggested for a packet data communication service in the future mobile communication system. That is, in consideration of limited radio resources, base station capacity and power consumption of an MS, a BS should secure a channel for data communication with another MS by releasing the channel for a non-data transmission period and rapidly reconnecting the channel when data transmission resumes. In addition, the BS should provide the MS with a function of controlling channel allocation duration, channel allocation action time, and channel allocation end time.
FIG. 1 is a diagram of transition between an active mode and a control hold mode in a traffic channel substate where traffic channel frames are communicated between an MS and a BS.
Referring to FIG. 1, an ERM (Extended Release Message), an ERMM (Extended Release Mini Message), and a UHDM (Universal Handoff Direction Message) are used for transition from the active mode to the control hold mode. An RAM (Resource Allocation Message), an RAMM (Resource Allocation Mini Message), an ESCAM (Extended Supplemental Channel Allocation Message), a Forward/Reverse SCAM (Supplemental Channel Allocation Message), and a UHDM are used for transition from the control hold mode to the active mode. An SCH can be allocated between the MS and the BS and gated transmission is not implemented on a reverse pilot channel in the active mode. On the other hand, the SCH is not allocated between the MS and the BS and the reverse pilot channel is gated-transmitted in the control hold state.
FIG. 2 illustrates a reference model as provided by the 3G IOS (Interoperability Specifications) for a digital air interface between an MSC and a BS and between BSs in a general mobile communication system.
Referring to FIG. 2, an A1 interface and an A2/A5 (exclusive for circuit data) are defined for transmitting a signal and user information respectively between an MSC 20 and a BSC 32. An A3 interface is defined to connect a target BS 40 to a frame selection/distribution function unit (SDU) 34 of a source BS 30 for soft/softer handoff between the BSs 30 and 40. Through the A3 interface are transmitted signaling and user data between the target BS 40 and the SDU 34 of the source BS 30. An A7 interface is defined to transmit/receive signals between the target BS 40 and the source BS 30 for soft/softer handoff between the BSs 30 and 40. An A8/A9 interface is used for transmitting signaling and user data between the source BS 30 and a PCF (Packet Control Function) block 50. A10 and A11 interfaces are defined to transmit signaling and user data between the PCF 50 and a PDSN (Packet data Serving Node) 60.
Wired communications links between BSs and between a BS 30 and an MSC in the CDMA mobile communication system are forward link directed from the MSC to the BS, a reverse link directed from the BS to the MSC, and link connected between the BSs. Specific procedures are performed in BSs and MSCs when packet data is transmitted within a BS, between the BSs, and between the MSCs.
FIG. 3 illustrates function mapping for state transition between modes shown in FIG. 1.
In FIG. 3, the function mapping is shown for the case that MAC and L2/L3 are given to a source BSC 32, an MS 2 is within the coverage area of the target BTS 40 after soft handoff, and the MS 2 or the BSs are transited from an active mode to a control hold mode or vice versa. Here, the source BS 30 is responsible for controlling a radio channel in use for the MS 2. Therefore, a signal for controlling the radio channel is transmitted through an A7 or A3 signal message. For example, when the active mode is transited to the control hold mode, an SCH used for communication between the MS 2 and a channel element 46 of the target BTS 40 should be released and the source BSC 32 should inform the target BTS 40 of information about gated transmission of a reverse pilot channel. On the other hand, upon transition from the control hold mode to the active mode, gated transmission of the reverse pilot channel is discontinued and an SCH is allocated to the MS 2 when necessary.
IMT-2000 standards are under development. However, this standardization work does not include definition of either a signal message (on the A7 interface) for mode transition between a BSC and an MS that belongs to a BTS (or a target BTS after soft handoff) or its related procedure. That is, no due consideration has been given to control of a corresponding physical channel for the case that an L3 signal message is generated for mode transition in a source BTS or an MS. For example, when an L3 signal message is generated, set-up and release of an FCH, a DCCH, and an SCH and designation of a reverse pilot channel gating rate has not been considered. As a result, a call is dropped at mode transition.
It is, therefore, an object of the present invention to provide a method and apparatus for controlling a corresponding physical channel upon mode transition at a BSC or a BTS in a mobile communication system.
It is another object of the present invention to provide a method and apparatus for controlling mode transition between a source BTS and an MS within the coverage area of a target BTS in a mobile communication system.
It is a further object of the present invention to provide a method and apparatus for generating a signal message to control mode transition between a BSC and a BTS or between a source BSC and a target BTS and performing a related procedure in a mobile communication system.
It is still another object of the present invention to provide a method and apparatus for preventing call drop at mode transition in a mobile communication system.
The above objects can be achieved by providing an apparatus and method for controlling mode transition in a traffic channel substate in a mobile communication system. If a control hold mode should be transited to an active mode a BSC sets a transmission rate on a DCCH in use to a continuous rate and transmits the continuous rate information to a BTS that an MS is within the coverage area of the BTS. Then, the BSC allocates an additional required channel besides the DCCH. If an active mode should be transited to a control hold mode, a BSC sets a transmission rate on a DCCH in use to a predetermined gating rate and transmits the gating rate information to a BTS that an MS is within the coverage area of the BTS. Then, the BSC releases an additional required channel besides the DCCH.